Wave attenuation mechanism and geometry optimization of a π-shaped porous floating breakwater: A numerical study

The expansion of offshore industries into deep-water environments necessitates a fundamental understanding of the fluid-structure interaction between surface gravity waves and permeable structures. This study investigates the wave attenuation mechanisms and energy dissipation characteristics of a π-shaped porous floating breakwater (PFB) through a macroscopic numerical framework based on the volume-averaged Reynolds-averaged Navier–Stokes equations. By modeling the porous matrix as a distributed body force within the momentum equations, this work demonstrates the utility of the macroscopic approach for the practical investigation of internal flow physics and geometric optimization of PFB. Our analysis reveals that wave energy dissipation is spatially non-uniform and is predominantly governed by frictional drag concentrated at the seaward part of PFB, where the relative velocity between the fluid and the pile-restrained skeleton is maximized. A distinct cyclic pattern of instantaneous dissipation is observed, synchronized with wave phases, where peak energy losses occur during the impingement of the wave crest and the strong reverse flow of the trough. The transition from a rectangular to a π-shaped cross section significantly modulates the internal energy dissipation rate. The deeper effective draft and the induction of wave overtopping enhance the dissipation efficiency of the upper regions. Notably, while the excavation of the lower cavity reduces the structural mass and the buoyancy-driven heave force, the π-shaped configuration maintains a heave response amplitude comparable to the rectangular baseline. This investigation elucidates the role of structural asymmetry in governing wave energy transport and highlights the effectiveness of macroscopic modeling in uncovering the underlying viscous-inertial mechanisms of porous floating systems.